1. Field of the Invention
The present invention relates to an equalizer of a vestigial sideband (VSB) digital television (DTV) receiver, and more particularly, to a method of initializing an equalizer of a VSB DTV receiver and an equalizer using the same.
2. Discussion of the Related Art
Generally, in a wireless data transceiving system, transmission signals are distorted by bandwidth-limited and multi-path channels, whereby an inter-symbol interference (ISI) is generated.
Such an ISI distorts transmission signals and causes bit errors in a receiver.
Accordingly, in order to restore signals distorted by an ISI, a receiver uses an equalizer and the equalizer needs to be firstly initialized.
FIG. 1 is a block diagram of a general VSB DTV system.
As shown in PIG. 1, the general VSB DTV system includes a transmitter 110 and a receiver 120 mutually connected by channels.
Here, the transmitter 110 encodes a signal and converts the encoded signal into an 8-level pulse amplitude modulation (PAM) signal by using a scrambler 111, a Reed-Solomon (RS) encoder 112, an interleaver 113 and a trellis coded modulation (TCM) encoder (Trellis encoder) 114.
Thereafter, the transmitter 110 multiplexes the 8-level PAM signal with a synchronization signal by using a multiplexer (MUX) 115, and inserts a pilot signal into the multiplexed signal by using a pilot inserter 116.
Then, the transmitter 110 filters and modulates the pilot signal-containing signal by using a VSB shaping filter 117 and a modulator 118, and transmits the resulting signal to the receiver 120.
The signal transmitted from the transmitter 110 to the receiver 120 is linearly distorted while passing through a channel.
In the receiver 120, the signal having passed through the channel is then converted into a baseband signal by a carrier recoverer 121. The resulting baseband signal is filtered by a RX (receive) filter 122, and the filtered signal is then synchronized by an interpolator 123, a timing recoverer 124 and a sync detector 125.
The synchronized signal is then equalized by an equalizer 126 for compensation of the signal for a linear distortion caused by a channel.
The receiver 120 then restores the equalized signal by using a phase tracker, a demultiplexer (DEMUX), a TCM decoder, a deinterleaver, an RS decoder and a descrambler.
At this time, the equalizer 126 is required to generate an output having a signal-to-noise ratio (SNR) as high as to enable viewers to view a DTV.
Accordingly, the equalizer 126 must be quickly initialized so that viewers cannot feel a delay time.
Instead of conventional DFE, a fractionally-spaced modified decision feedback equalizer (FS-MDFE) can be used in a DTV receiver.
FIG. 2 is a block diagram of an FS-MDFE.
A general DFE firstly performs a signal processing in a forward filter for removing a precursor, an interference component caused by symbols behind a current symbol, and then performs a signal processing in a backward filter for removing a postcursor, an interference component caused by symbols before the current symbol.
On the contrary, as shown in FIG. 2, the FS-MDFE firstly performs a signal processing in a backward filter, and then performs a signal processing in a forward filter.
The FS-MDFE estimates channel properties, and then can easily initialize a coefficient of a backward filter by using the estimated channel properties.
Accordingly, in case that an equalizer is initialized by training, the FS-MDFE needs to train only a coefficient of a forward filter, and therefore has a short initialization time.
An operation of the FS-MDFE will now be described in detail with reference to FIG. 2.
Referring to FIG. 2, in the FS-MDFE, an input 210 of a forward filter is reduced by a postcursor component 220 calculated by a backward filter, and then the resulting value is stored in a first memory of the forward filter.
These values are sequentially stored in respective memories 230 of the forward filter, wherein each value is reduced by a multiplication of a backward filter coefficient 240 connected to each memory 230 and an already-detected symbol 260 stored in each backward filter memory 250.
Then, this subtracted value is removed in calculating a postcursor component that should be removed at each forward filter tap through a backward filter signal processing.
The so-obtained value 270 is multiplied by each forward filter coefficient 280, and a polyphase sum value of the resulting values becomes an input (Zn) 291 of a slicer 292.
Then, outputs 293 of the slicer 292 are sequentially stored in the backward filter.
By repetition of the aforementioned processes, a signal transmitted from a transmitter can be obtained from the output 293 of the slicer 292.
Here, it is assumed that forward filter coefficients were initialized. However, in practice, forward filter coefficients need to be properly initialized.
For a method of initializing the FS-MDFE, there is a method using a LMS (Least Mean Square) training technique.
However, in case of this method, since a training signal is very short in length compared with a data signal, a forward filter of the FS-MDFE cannot be initialized only by the training signal.
Also, for a method of initializing the FS-MDFE, there is an MMSE (Minimum Mean Squared Error) initialization method. However, this method cannot be practically used owing to high packaging complexity caused by an inverse operation of a matrix.